In the conventional process of manufacturing a polypropylene sheet, using polypropylene type resin as raw material, the sheet is generally cooled for the purpose of improving its transparency. However, when the sheet has a thickness exceeding 50 μm, a technique of adding a nucleating agent is employed to improve the transparency because it is difficult to uniformly cool such a thick sheet and attain a satisfactory level of transparency.
However, a polypropylene sheet molded by adding a nucleating agent shows an enhanced level of crystallinity because of an increase of the number of defective crystals and that of spherulites. Then, as a result, the softening point of the sheet rises to by turn give rise to a problem that, when applying heat to the polypropylene sheet for secondary processing (thermoforming), the processing temperature range becomes narrowed to make the thermoforming very difficult.
Then, a special forming apparatus is required to thermoform a transparent polypropylene sheet and this problem has prevented the scope of application of products of thermoformed transparent polypropylene sheets from expanding.
An object of the present invention is to provide a low crystallizability polypropylene sheet that can be thermoformed with ease at low temperature without employing a special forming apparatus and secure an enhanced level of transparency and luster after forming.